This pack of 4 razor-sharp, double-sided, rounded-tip ceramic box cutter replacement blades is for use only with the Slice¢ ceramic box cutter. These blades are rated 8.2 on the Mohs hardness scale (two steps below diamond) compared to metal knives rated at just 5.5. Harder edges mean sharper edges that maintain sharpness longer, cut better, and require sharpening far less frequently. In fact, depending on use, you can go years without sharpening ceramic blades and they never rust. And the rounded-tip makes them safer than traditional metal.